Solid electrolyte material and battery

ABSTRACT

A solid electrolyte material includes a first crystal phase. The first crystal phase has a composition that is deficient in Li as compared with a composition represented by the following composition formula (1). 
       Li 3 Y 1 Cl 6   formula (1)

BACKGROUND 1. Technical Field

The present disclosure relates to a solid electrolyte material and abattery.

2. Description of the Related Art

Japanese Unexamined Patent Application Publication No. 2011-129312discloses an all-solid-state battery containing a sulfide solidelectrolyte.

Japanese Unexamined Patent Application Publication No. 2006-244734discloses an all-solid-state battery that includes an indium-containinghalide as a solid electrolyte.

Z. anorg. allg. Chem. 623 (1997) 1067 discloses Li₃YCl₆.

SUMMARY

In one general aspect, the techniques disclosed here feature a solidelectrolyte material that includes a first crystal phase. The firstcrystal phase has a composition that is deficient in Li as compared witha composition represented by the following composition formula (1).

Li₃Y₁Cl₆  formula (1)

Additional benefits and advantages of the disclosed embodiments willbecome apparent from the specification and drawings. The benefits and/oradvantages may be individually obtained by the various embodiments andfeatures of the specification and drawings, which need not all beprovided in order to obtain one or more of such benefits and/oradvantages.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view of a battery according to asecond embodiment;

FIG. 2A is a view of the crystal structure of a Li₃YbCl₆ structure;

FIG. 2B is a view of the crystal structure of a Li₃YbCl₆ structure;

FIG. 3 is a schematic view of a method for evaluating ionicconductivity;

FIG. 4 is a graph of the temperature dependence of the ionicconductivity of solid electrolytes;

FIG. 5 is a graph of XRD patterns; and

FIG. 6 is a graph of initial discharging characteristics.

DETAILED DESCRIPTION

Embodiments of the present disclosure are described below with referenceto the accompanying drawings.

First Embodiment

A solid electrolyte material according to a first embodiment is a solidelectrolyte material including a first crystal phase.

The first crystal phase has a composition that is deficient in Li ascompared with a composition represented by the following compositionformula (1). The first crystal phase may have a composition including aLi deficiency in the following composition formula (1).

Li₃Y₁Cl₆  formula (1)

A solid electrolyte material (for example, a halide solid electrolytematerial) with such a structure can have high lithium ion conductivity.Such a solid electrolyte material can have a stable structure in theexpected operating temperature range of the battery (for example, −30°C. to 80° C.). The solid electrolyte material according to the firstembodiment does not have a structure in which the phase transitiontemperature is in the operating temperature range of the battery (forexample, a structure described in Japanese Unexamined Patent ApplicationPublication No. 2006-244734). Thus, the solid electrolyte materialaccording to the first embodiment can stably maintain high ionicconductivity without causing a phase transition in the operatingtemperature range of the battery even in a temperature changingenvironment.

With such a structure, the solid electrolyte material according to thefirst embodiment can be used to provide an all-solid-state secondarybattery with good charge-discharge characteristics. The solidelectrolyte material according to the first embodiment can also be usedto provide a sulfur-free all-solid-state secondary battery. The solidelectrolyte material according to the first embodiment does not have astructure that generates hydrogen sulfide when exposed to the atmosphere(for example, a structure described in Japanese Unexamined PatentApplication Publication No. 2011-129312). An all-solid-state secondarybattery thus produced generates no hydrogen sulfide and has improvedsafety.

In the solid electrolyte material according to the first embodiment, thefirst crystal phase may be represented by the following compositionformula (2).

Li_(3−3δ)Y_(1+δ)Cl₆  formula (2)

0≤δ≤0.15

A solid electrolyte material with such a structure can have higherlithium ion conductivity.

In the solid electrolyte material according to the first embodiment, thecomposition formula (2) may satisfy 0.01≤δ≤0.133.

A solid electrolyte material with such a structure can have higherlithium ion conductivity.

In the solid electrolyte material according to the first embodiment, thesolid electrolyte material may have an X-ray diffraction pattern thatincludes a peak in each of a first range, a second range, and a thirdrange, the X-ray diffraction pattern being measured using Cu-Kαradiation as an X-ray source. In the first range, a diffraction angle 2θis 30.34 degrees or more and 32.36 degrees or less.

In the second range, the diffraction angle 2θ is 39.51 degrees or moreand 42.07 degrees or less. In the third range, the diffraction angle 2θis 47.18 degrees or more and 50.30 degrees or less.

A solid electrolyte material with such a structure can have higherlithium ion conductivity.

In the solid electrolyte material according to the first embodiment, theX-ray diffraction pattern further may include a peak in a fourth rangein which the diffraction angle 2θ is 15.2 degrees or more and 16.23degrees or less and include a peak in a fifth range in which thediffraction angle 2θ is 52.4 degrees or more and 54.6 degrees or less.

A solid electrolyte material with such a structure can have higherlithium ion conductivity.

To obtain an X-ray diffraction pattern, X-ray diffraction may bemeasured by a θ-2θ method using Cu-Kα radiation (wavelengths of 1.5405and 1.5444 angstroms) as X-rays. When the measured intensity isinsufficient, part of the above peaks may not be observed. An X-raysource other than Cu-Kα radiation may also be used. In such a case, itgoes without saying that the above diffraction angles 2θ can beconverted by the Bragg equation (2d sin(θ)=λd: interplanar spacing, θ:diffraction angle, λ: the wavelength of X-rays).

The first crystal phase in which a peak is observed in the above 20range is not limited to a particular crystal structure and may have thefollowing crystal structure, for example.

One of such crystal structures is a Li₃YbCl₆ (hereinafter also referredto as LYC) structure with a crystal structure belonging to the spacegroup Pnma, wherein the lattice constants of the unit cell are a=12.67to 13.19 angstroms, b=10.98 to 11.44 angstroms, c=5.91 to 6.16angstroms, α=90 degrees, β=90 degrees, and γ=90 degrees.

Another crystal structure may be a Li₃ErCl₆ structure with a crystalstructure belonging to the space group P-3m1, wherein the latticeconstants of the unit cell are a=10.97 to 11.5 angstroms, b=a, c=5.9 to6.2 angstroms, α=90 degrees, β=90 degrees, and γ=120 degrees.

In particular, the crystal structure may have almost the samearrangement of chlorine as in the Li₃YbCl₆ or Li₃ErCl₆ structure, thatis, may have a chlorine sublattice with an atomic arrangement of adistorted hexagonal close-packed structure.

In other words, the first crystal phase may contain a chlorinesublattice, and the arrangement of chlorine in the sublattice maycontain an atomic arrangement of a distorted hexagonal close-packedstructure.

A solid electrolyte material with such a structure can have higherlithium ion conductivity.

The first crystal phase may contain the atomic arrangement of theLi₃YbCl₆ structure.

A solid electrolyte material with such a structure can have higherlithium ion conductivity.

FIGS. 2A and 2B illustrate the crystal structure of the Li₃YbCl₆structure.

FIG. 2A is a perspective view of the crystal structure of the Li₃YbCl₆structure.

FIG. 2B is a top view of the crystal structure of the Li₃YbCl₆ structureprojected in the c-axis direction.

As illustrated in FIGS. 2A and 2B, the Li₃YbCl₆ structure (LYCstructure) has the symmetry of the orthorhombic crystal system andbelongs to the space group Pnma. In the characteristic Li₃YbCl₆structure, the chlorine sublattice has an atomic arrangement of adistorted hexagonal close-packed structure. More specifically, in theabc axes defined in FIG. 2, six chlorine atoms in almost the same abplanes have an interatomic distance in the range of 3.6 to 3.9 angstromsand a bond angle of 60±5 degrees. The chlorine atoms in the ab planesare alternately located at almost the same atomic positions in thec-axis direction. The detailed atomic arrangement is described in theinorganic crystal structure database (ICSD).

A solid electrolyte material with such a structure can have higherlithium ion conductivity. More specifically, in a crystal structure likethe first crystal phase, Cl is more strongly attracted to the vicinityof Y. This forms a lithium ion diffusion path. Furthermore, anunoccupied site is formed in the Li-deficient composition andfacilitates lithium ion conduction. Thus, it is surmised that lithiumion conductivity is further improved.

The X-ray diffraction pattern of the solid electrolyte materialaccording to the first embodiment may satisfy FWHM/2θ_(p)≤0.01, whereFWHM denotes a full width at half maximum of the peak in the firstrange, and 2θ_(p) denotes a central value of the peak.

A solid electrolyte material with such a structure can have higherlithium ion conductivity.

The FWHM is the full width at half maximum of an X-ray diffraction peakat the above 2θ=30.34 to 32.36 degrees measured by the X-raydiffractometry.

The 2θ_(p) is the diffraction angle at the center of the X-raydiffraction peak (peak central value).

In the solid electrolyte material according to the first embodiment, thefirst crystal phase may have a distorted structure, and the atoms may belocated at slightly different positions.

The solid electrolyte material according to the first embodiment mayhave a different crystal phase with a different crystal structure fromthe first crystal phase.

The different crystal phase may be located between the first crystalphases.

The different crystal phase may include a second crystal phase with aLiCl parent structure.

A solid electrolyte material with such a structure can have higherlithium ion conductivity.

The second crystal phase may have an X-ray diffraction pattern thatincludes a peak in at least one range selected from the group consistingof a range in which a diffraction angle 2θ is 29.18 degrees or more and31.03 degrees or less and a range in which the diffraction angle 2θ is33.83 degrees or more and 36.00 degrees or less, the X-ray diffractionpattern being measured by the θ-2θ method using Cu-Kα radiation(wavelengths of 1.5405 and 1.5444 angstroms) as an X-ray source. Thesecond crystal phase may have an X-ray diffraction pattern that includesa peak at a diffraction angle 2θ in the range of 29.18 to 31.03 degreesand a peak at a diffraction angle 2θ in the range of 33.83 to 36.00degrees.

A solid electrolyte material with such a structure can have higherlithium ion conductivity.

The second crystal phase having a peak in the above 20 range may have arock-salt structure belonging to the space group Fm-3m, wherein thelattice constants of the unit cell are a=b=c=5.13 angstroms and α=β=γ=90degrees.

The different crystal phase may include a third crystal phase with aYCl₃ parent structure.

A solid electrolyte material with such a structure can have higherlithium ion conductivity.

The third crystal phase may have an X-ray diffraction pattern thatincludes a peak in at least one range selected from the group consistingof a range in which a diffraction angle 2θ is 14.34 degrees or more and15.23 degrees or less and a range in which the diffraction angle 2θ is25.65 degrees or more and 27.26 degrees or less, the X-ray diffractionpattern being measured by the θ-2θ method using Cu-Kα radiation(wavelengths of 1.5405 and 1.5444 angstroms) as an X-ray source. Thethird crystal phase may have an X-ray diffraction pattern that includesa peak at a diffraction angle 2θ in the range of 14.34 to 15.23 degreesand a peak at a diffraction angle 2θ in the range of 25.65 to 27.26degrees.

A solid electrolyte material with such a structure can have higherlithium ion conductivity.

The third crystal phase having a peak in the above 20 range may have astructure belonging to the space group C2/m, wherein the latticeconstants of the unit cell are a=6.92 angstroms, b=11.94 angstroms,c=6.44 angstroms, β=90 degrees, β=111 degrees, and γ=90 degrees.

The different crystal phase is not limited to the second crystal phaseor the third crystal phase and may be another crystal phase.

The solid electrolyte material according to the first embodiment mayhave an amorphous phase.

The solid electrolyte material according to the first embodiment mayhave any shape, for example, acicular, spherical, or ellipsoidal. Forexample, the solid electrolyte material according to the firstembodiment may be particles. Particles may be stacked and then pressedto form pellets or a sheet.

For example, a particulate (for example, spherical) solid electrolytematerial according to the first embodiment may have a median size in therange of 0.1 to 100 μm.

In the first embodiment, the median size may range from 0.5 to 10 μm.

Such a structure can further increase ionic conductivity. Furthermore,the solid electrolyte material according to the first embodiment and anactive material can be more satisfactorily dispersed.

In the first embodiment, the solid electrolyte material may be smallerthan the median size of the active material.

Such a structure enables the solid electrolyte material according to thefirst embodiment and the active material to be more satisfactorilydispersed.

The phrase “a specified value A ranges from B to C”, as used herein,refers to “a range of B≤A≤C”.

<Method for Producing Solid Electrolyte Material>

The solid electrolyte material according to the first embodiment can beproduced by the following method, for example.

Raw powders of a binary halide are prepared at a blend ratio of thedesired composition. For example, to prepare Li₃YCl₆, LiCl and YCl₃ areprepared at a mole ratio of approximately 3:1. In consideration of avariation in composition in the synthesis process, the blend ratio maybe adjusted in advance to offset the variation.

The mixing ratio of the raw powders can be altered to adjust the ratioof a Li (lithium) deficient crystal phase in the composition formula(1). For example, “S” in the composition formula (2) can be altered.

The raw powders are blended well and are then mixed, ground, and reactedby a mechanochemical milling method. It may be followed by firing in avacuum or in an inert atmosphere. Alternatively, the raw powders may beblended well and fired in a vacuum or in an inert atmosphere. The firingconditions may be 100° C. to 650° C. for 1 hour or more.

Thus, a solid electrolyte material including a crystal phase asdescribed above is produced.

The raw material ratio and the reaction method and the reactionconditions of the raw powders can be adjusted for the crystal phasestructure and crystal structure in the solid electrolyte material andthe peak position in an X-ray diffraction pattern measured using Cu-Kαas a radiation source.

Second Embodiment

The second embodiment is described below. The contents described in thefirst embodiment may be appropriately omitted to avoid overlap.

A battery according to the second embodiment contains the solidelectrolyte material described in the first embodiment.

The battery according to the second embodiment includes the solidelectrolyte material, a positive electrode, a negative electrode, and anelectrolyte layer.

The electrolyte layer is located between the positive electrode and thenegative electrode.

At least one of the positive electrode, the electrolyte layer, and thenegative electrode contains the solid electrolyte material according tothe first embodiment.

Such a structure can improve the charge-discharge characteristics of thebattery.

A specific example of the battery according to the second embodiment isdescribed below.

FIG. 1 is a schematic cross-sectional view of a battery 1000 accordingto the second embodiment.

The battery 1000 according to the second embodiment includes a positiveelectrode 201, a negative electrode 203, and an electrolyte layer 202.

The positive electrode 201 contains positive-electrode active materialparticles 204 and solid electrolyte particles 100.

The electrolyte layer 202 is located between the positive electrode 201and the negative electrode 203.

The electrolyte layer 202 contains an electrolyte material (for example,a solid electrolyte material).

The negative electrode 203 contains negative-electrode active materialparticles 205 and the solid electrolyte particles 100.

The solid electrolyte particles 100 are particles of the solidelectrolyte material according to the first embodiment or particlescomposed mainly of the solid electrolyte material according to the firstembodiment.

The positive electrode 201 contains a material that can adsorb anddesorb metal ions (for example, lithium ions). The positive electrode201 contains a positive-electrode active material (for example, thepositive-electrode active material particles 204), for example.

Examples of the positive-electrode active material includelithium-containing transition metal oxides (for example, Li(NiCoAl)O₂,LiCoO₂, etc.), transition metal fluorides, polyanion and fluorinatedpolyanion materials, transition metal sulfides, transition metaloxyfluorides, transition metal oxysulfides, and transition metaloxynitrides.

The positive-electrode active material particles 204 may have a mediansize in the range of 0.1 to 100 μm. The positive-electrode activematerial particles 204 with a median size of less than 0.1 μm in thepositive electrode, together with a halide solid electrolyte material,may not achieve a satisfactory dispersion state.

This results in the battery with poor charge-discharge characteristics.The positive-electrode active material particles 204 with a median sizeof more than 100 μm results in slow lithium diffusion in thepositive-electrode active material particles 204. This may make thehigh-power operation of the battery difficult.

The positive-electrode active material particles 204 may have a largermedian size than the halide solid electrolyte material. In such a case,the positive-electrode active material particles 204 and the halidesolid electrolyte material can achieve a satisfactory dispersion state.

The volume ratio “v:100-v” of the positive-electrode active materialparticles 204 to the halide solid electrolyte material in the positiveelectrode 201 may satisfy 30≤v≤95. v<30 may result in the battery withan insufficient energy density. v>95 may make high-power operationdifficult.

The positive electrode 201 may have a thickness in the range of 10 to500 μm. The positive electrode 201 with a thickness of less than 10 μmmay result in the battery with an insufficient energy density. Thepositive electrode 201 with a thickness of more than 500 μm may makehigh-power operation difficult.

The electrolyte layer 202 contains an electrolyte material. Theelectrolyte material is a solid electrolyte material, for example. Thus,the electrolyte layer 202 may be a solid electrolyte layer.

The solid electrolyte layer may contain the solid electrolyte materialaccording to the first embodiment as a main component. Morespecifically, the weight ratio of the solid electrolyte materialaccording to the first embodiment to the solid electrolyte layer is 50%or more (50% or more by weight), for example.

Such a structure can further improve the charge-dischargecharacteristics of the battery.

The weight ratio of the solid electrolyte material according to thefirst embodiment to the solid electrolyte layer is 70% or more (70% ormore by weight), for example.

Such a structure can further improve the charge-dischargecharacteristics of the battery.

In addition to the solid electrolyte material according to the firstembodiment contained as a main component, the solid electrolyte layermay contain incidental impurities, or starting materials for thesynthesis of the solid electrolyte material, by-products, anddegradation products.

The weight ratio of the solid electrolyte material according to thefirst embodiment to the solid electrolyte layer except incidentalimpurities may be 100% (100% by weight).

Such a structure can further improve the charge-dischargecharacteristics of the battery.

Thus, the solid electrolyte layer may be composed of the solidelectrolyte material according to the first embodiment alone.

Alternatively, the solid electrolyte layer may be composed only of asolid electrolyte material different from the solid electrolyte materialaccording to the first embodiment. The solid electrolyte materialdifferent from the solid electrolyte material according to the firstembodiment is Li₂MgX₄, Li₂FeX₄, Li(Al, Ga, In)X₄, Li₃(Al, Ga, In)X₆, orLiI (X: Cl, Br, I), for example.

The solid electrolyte layer may contain both the solid electrolytematerial according to the first embodiment and the solid electrolytematerial different from the solid electrolyte material according to thefirst embodiment. Both of them may be uniformly dispersed. A layer ofthe solid electrolyte material according to the first embodiment and alayer of the solid electrolyte material different from the solidelectrolyte material according to the first embodiment may be located inorder in the lamination direction of the battery.

The solid electrolyte layer may have a thickness in the range of 1 to1000 μm. The solid electrolyte layer with a thickness of less than 1 μmis more likely to cause a short circuit between the positive electrode201 and the negative electrode 203. The solid electrolyte layer with athickness of more than 1000 μm may make high-power operation difficult.

The negative electrode 203 contains a material that can adsorb anddesorb metal ions (for example, lithium ions). The negative electrode203 contains a negative-electrode active material (for example, thenegative-electrode active material particles 205), for example.

The negative-electrode active material may be a metallic material,carbon material, oxide, nitride, tin compound, or silicon compound. Themetallic material may be a single metal. Alternatively, the metallicmaterial may be an alloy. Examples of the metallic material includelithium metal and lithium alloys. Examples of the carbon materialinclude natural graphite, coke, carbon during graphitization, carbonfiber, spherical carbon, artificial graphite, and amorphous carbon. Fromthe perspective of capacity density, silicon (Si), tin (Sn), siliconcompounds, and tin compounds may be used. The use of anegative-electrode active material with a low average reaction voltageenhances the electrolysis-suppressing effect of the solid electrolytematerial according to the first embodiment.

The negative-electrode active material particles 205 may have a mediansize in the range of 0.1 to 100 μm. The negative-electrode activematerial particles 205 with a median size of less than 0.1 μm in thenegative electrode, together with the solid electrolyte particles 100,may not achieve a satisfactory dispersion state. This results in thebattery with poor charge-discharge characteristics. Thenegative-electrode active material particles 205 with a median size ofmore than 100 μm results in slow lithium diffusion in thenegative-electrode active material particles 205. This may make thehigh-power operation of the battery difficult.

The negative-electrode active material particles 205 may have a largermedian size than the solid electrolyte particles 100. In such a case,the negative-electrode active material particles 205 and the halidesolid electrolyte material can achieve a satisfactory dispersion state.

The volume ratio “v:100-v” of the negative-electrode active materialparticles 205 to the solid electrolyte particles 100 in the negativeelectrode 203 may satisfy 30≤v≤95. v<30 may result in the battery withan insufficient energy density. v>95 may make high-power operationdifficult.

The negative electrode 203 may have a thickness in the range of 10 to500 μm. A negative electrode with a thickness of less than 10 μm mayresult in a battery with an insufficient energy density. A negativeelectrode with a thickness of more than 500 μm may make high-poweroperation difficult.

At least one of the positive electrode 201, the electrolyte layer 202,and the negative electrode 203 may contain a sulfide solid electrolyteor an oxide solid electrolyte to improve ionic conductivity, chemicalstability, or electrochemical stability. The sulfide solid electrolytemay be Li₂S—P₂S₅, Li₂S—SiS₂, Li₂S—B₂S₃, Li₂S—GeS₂,Li_(3.25)Ge_(0.25)P_(0.75)S₄, or Li₁₀GeP₂S₁₂. The oxide solidelectrolyte may be a NASICON-type solid electrolyte, exemplified byLiTi₂(PO₄)₃ or an element-substituted product thereof, a (LaLi)TiO₃perovskite solid electrolyte, a LISICON-type solid electrolyte,exemplified by Li₁₄ZnGe₄O₁₆, Li₄SiO₄, LiGeO₄, or an element-substitutedproduct thereof, a garnet solid electrolyte, exemplified by Li₇La₃Zr₂O₁₂or an element-substituted product thereof, Li₃N or a H-substitutedproduct thereof, or Li₃PO₄ or a N-substituted product thereof.

At least one of the positive electrode 201, the electrolyte layer 202,and the negative electrode 203 may contain an organic polymer solidelectrolyte to improve ionic conductivity. The organic polymer solidelectrolyte may be a compound of a polymer and a lithium salt. Thepolymer may have an ethylene oxide structure. The ethylene oxidestructure can increase the lithium salt content and ionic conductivity.Examples of the lithium salt include LiPF₆, LiBF₄, LiSbF₆, LiAsF₆,LiSO₃CF₃, LiN(SO₂CF₃)₂, LiN(SO₂C₂F₅)₂, LiN(SO₂CF₃)(SO₂C₄F₉), andLiC(SO₂CF₃)₃. A lithium salt selected from these may be used alone. Amixture of two or more lithium salts selected from these may also beused.

At least one of the positive electrode 201, the electrolyte layer 202,and the negative electrode 203 may contain a non-aqueous electrolytesolution, a gel electrolyte, or an ionic liquid to facilitate lithiumion transfer and improve the output characteristics of the battery.

The non-aqueous electrolyte solution contains a non-aqueous solvent anda lithium salt dissolved in the non-aqueous solvent. Examples of thenon-aqueous solvent include cyclic carbonate solvents, chain carbonatesolvents, cyclic ether solvents, chain ether solvents, cyclic estersolvents, chain ester solvents, and fluorinated solvents. Examples ofthe cyclic carbonate solvents include ethylene carbonate, propylenecarbonate, and butylene carbonate.

Examples of the chain carbonate solvents include dimethyl carbonate,ethyl methyl carbonate, and diethyl carbonate. Examples of the cyclicether solvents include tetrahydrofuran, 1,4-dioxane, and 1,3-dioxolane.Examples of the chain ether solvents include 1,2-dimethoxyethane and1,2-diethoxyethane. Examples of the cyclic ester solvents includeγ-butyrolactone. Examples of the chain ester solvents include methylacetate. Examples of the fluorinated solvents include fluoroethylenecarbonate, methyl fluoropropionate, fluorobenzene, fluoroethyl methylcarbonate, and fluorodimethylene carbonate. One non-aqueous solventselected from these may be used alone. A combination of two or morenon-aqueous solvents selected from these may also be used. Thenon-aqueous electrolyte solution may contain at least one fluorinatedsolvent selected from the group consisting of fluoroethylene carbonate,methyl fluoropropionate, fluorobenzene, fluoroethyl methyl carbonate,and fluorodimethylene carbonate. Examples of the lithium salt includeLiPF₆, LiBF₄, LiSbF₆, LiAsF₆, LiSO₃CF₃, LiN(SO₂CF₃)₂, LiN(SO₂C₂F₅)₂,LiN(SO₂CF₃)(SO₂C₄F₉), and LiC(SO₂CF₃)₃. A lithium salt selected fromthese may be used alone. A mixture of two or more lithium salts selectedfrom these may also be used. The concentration of the lithium saltranges from 0.5 to 2 mol/I, for example.

The gel electrolyte may be a polymer material containing a non-aqueouselectrolyte solution. The polymer material may be poly(ethylene oxide),polyacrylonitrile, poly(vinylidene difluoride), poly(methylmethacrylate), or a polymer having an ethylene oxide bond.

A cation in the ionic liquid may be an aliphatic chain quaternary salt,such as tetraalkylammonium or tetraalkylphosphonium, an alicyclicammonium, such as pyrrolidinium, morpholinium, imidazolinium,tetrahydropyrimidinium, piperazinium, or piperidinium, or anitrogen-containing heteroaromatic cation, such as pyridinium orimidazolium. An anion in the ionic liquid may be PF₆ ⁻, BF₄ ⁻, SbF⁻,AsF⁻, SO₃CF₃ ⁻, N(SO₂CF₃)₂ ⁻, N(SO₂C₂F₅)₂ ⁻, N(SO₂CF₃)(SO₂C₄F₉)⁻, orC(SO₂CF₃)₃. The ionic liquid may contain a lithium salt.

At least one of the positive electrode 201, the electrolyte layer 202,and the negative electrode 203 may contain a binder to improve adhesionbetween particles. The binder is used to improve the binding property ofa material constituting the electrode. Examples of the binder includepolyvinylidene difluoride, polytetrafluoroethylene, polyethylene,polypropylene, aramid resin, polyamide, polyimide, polyamideimide,polyacrylonitrile, polyacrylic acid, methyl polyacrylate ester, ethylpolyacrylate ester, hexyl polyacrylate ester, polymethacrylic acid,methyl polymethacrylate ester, ethyl polymethacrylate ester, hexylpolymethacrylate ester, polyvinyl acetate, polyvinylpyrrolidone,polyether, polyethersulfone, hexafluoropolypropylene, styrene-butadienerubber, and carboxymethylcellulose. Other examples of the binder includecopolymers of two or more materials selected from tetrafluoroethylene,hexafluoroethylene, hexafluoropropylene, perfluoroalkyl vinyl ether,vinylidene fluoride, chlorotrifluoroethylene, ethylene, propylene,pentafluoropropylene, fluoromethyl vinyl ether, acrylic acid, andhexadiene. A mixture of two or more selected from these may also be usedas a binder.

At least one of the positive electrode 201 and the negative electrode203 may contain a conductive agent, if necessary.

The conductive agent is used to reduce the electrode resistance.Examples of the conductive agent include graphite, such as naturalgraphite and artificial graphite, carbon black, such as acetylene blackand Ketjen black, electrically conductive fiber, such as carbon fiberand metal fiber, metal powders, such as fluorocarbon and aluminum,electrically conductive whiskers, such as zinc oxide and potassiumtitanate, electrically conductive metal oxides, such as titanium oxide,and electrically conductive polymers, such as polyaniline, polypyrrole,and polythiophene. The use of a carbon conductive agent as theconductive agent can reduce costs.

The battery according to the second embodiment may be of various types,such as a coin type, a cylindrical type, a square or rectangular type, asheet type, a button type, a flat type, or a layered type.

EXAMPLES

The present disclosure is described in detail in the following examplesand comparative examples.

Example 1 [Preparation of Solid Electrolyte Material]

Raw powders LiCl and YCl₃ were weighed at a mole ratio ofLiCl:YCl₃=2.7:1.1 in an argon atmosphere with a dew point of −60° C. orless. The raw powders were ground and mixed in a mortar. The mixture wasthen milled in a planetary ball mill at 600 rpm for 25 hours. Themixture was fired in an Ar (argon) atmosphere in a furnace at 400° C.for 48 hours.

Thus, a powder of a solid electrolyte material containing a Li-deficientcrystal phase according to Example 1 was prepared.

[Evaluation of Lithium Ion Conductivity]

FIG. 3 is a schematic view of a method for evaluating ionicconductivity.

A press forming die 300 includes an electronically insulatedpolycarbonate frame 301, an electron-conductive stainless steel upperpunch 303, and an electron-conductive stainless steel lower punch 302.

The apparatus illustrated in FIG. 3 was used to evaluate ionicconductivity by the following method.

The powder of the solid electrolyte material according to Example 1 wasloaded in the press forming die 300 in a dry atmosphere with a dew pointof −30° C. or less and was uniaxially pressed at 400 MPa to produce aconductivity measurement cell according to Example 1.

Under pressure, the upper punch 303 and the lower punch 302 were coupledthrough a lead wire to a potentiostat (Princeton Applied Research,VersaSTAT4) equipped with a frequency response analyzer. The ionicconductivity at room temperature was measured by an electrochemicalimpedance measurement method.

The ionic conductivity of the solid electrolyte material according toExample 1 measured at 22° C. was 3.0×10⁻⁴ S/cm.

[Evaluation of Phase Transition]

FIG. 4 is a graph of the temperature dependence of the ionicconductivity of solid electrolytes.

The results in FIG. 4 were obtained by the following method.

The conductivity measurement cell according to Example 1 was placed in athermostatic chamber. The temperature dependence of conductivity wasmeasured at a temperature in the range of −20° C. to 80° C. duringtemperature rise and drop.

As shown in FIG. 4, a sudden change in conductivity indicating a phasechange (that is, phase transition) was not observed.

[Analysis of Crystal Structure]

FIG. 5 is a graph of XRD patterns.

The results in FIG. 5 were obtained by the following method.

To analyze the crystal structure of a solid electrolyte, the X-raydiffraction pattern of the solid electrolyte was measured with an X-raydiffractometer (Rigaku Corporation, MiniFlex600) in a dry environmentwith a dew point of −45° C. or less. Cu-Kα radiation was used as anX-ray source. More specifically, the X-ray diffraction was measured bythe θ-2θ method using Cu-Kα radiation (wavelengths of 1.5405 and 1.5444angstroms) as X-rays.

In the X-ray diffraction pattern of Example 1, relatively intense peakswere observed at 15.74, 31.28, 40.76, 48.68, 53.46, and 59.08 degrees.

These peaks corresponded approximately to part of the peak positions ofthe X-ray diffraction pattern of an LYC phase with lattice constantsa=12.94 angstroms, b=11.21 angstroms, c=6.06 angstroms, α=90 degrees,β=90 degrees, and γ=90 degrees.

The relationship FWHM/2θ_(p) between the full width at half maximum(FWHM) and the peak central value 2θ_(p) of the peak at 20=31.28 degreeswas 0.68%.

A peak indicating the presence of a phase other than the first crystalphase, such as a diffraction peak derived from LiCl or a diffractionpeak derived from YCl₃, was not observed.

The Li content per unit weight of the solid electrolyte materialaccording to Example 1 was measured by atomic absorption spectrometry,and the Y content was measured by ICP emission spectrometry. The Li andY contents were converted to the mole ratio x_(Li,Total)/x_(Y,Total).x_(Li,Total)/x_(Y,Total) was 2.62. Thus, the solid electrolyte materialaccording to Example 1 had a composition formula including aLi-deficient first crystal phase represented by the composition formulaLi_(2.80)Y_(1.07)Cl₆.

[Production of Secondary Battery]

The solid electrolyte material according to Example 1 and an activematerial LiCoO₂ were weighed at a volume ratio of 70:30 in an argonglove box.

They were mixed in an agate mortar to prepare a mixture.

The solid electrolyte material according to Example 1 in an amountcorresponding to a thickness of 700 μm, 8.5 mg of the mixture, and 11.5mg of an Al powder were stacked in this order in an insulating tube. Thestack was pressed at 300 MPa to prepare a first electrode and a solidelectrolyte layer.

Subsequently, a metal In (thickness: 200 μm) was placed on a surface ofthe solid electrolyte layer opposite the first electrode. The stack waspressed at a pressure of 80 MPa to prepare a laminate composed of thefirst electrode, the solid electrolyte layer, and a second electrode.

Subsequently, a stainless steel current collector was placed on the topand bottom of the laminate and was coupled to a collector lead.

Finally, the interior of the insulating tube was sealed with aninsulating ferrule and was isolated from the outside atmosphere.

Thus, a secondary battery according to Example 1 was produced.

[Charge-Discharge Test]

FIG. 6 is a graph of initial discharging characteristics.

The results in FIG. 6 were obtained by the following method.

The secondary battery according to Example 1 was placed in athermostatic chamber at 25° C.

The battery was charged to a voltage of 3.6 Vat a constant current rateof 0.05 C (20 hour rate) with respect to its theoretical capacity.

The battery was then discharged to a voltage of 1.9 V at the samecurrent rate of 0.05 C.

The measurements showed that the secondary battery according to Example1 had an initial discharge capacity of 596 μAh.

Example 2

Raw powders LiCl and YCl₃ of a solid electrolyte were mixed at a moleratio of LiCl:YCl₃=2.85:1.05.

Except for this, the synthesis, evaluation, and analysis were performedin the same manner as in Example 1.

The ionic conductivity measured at 22° C. was 1.8×10⁻⁴ S/cm.

A sudden change in conductivity indicating a phase change (that is,phase transition) was not observed at a temperature in the range of −30°C. to 80° C.

FIG. 5 shows an XRD pattern of a solid electrolyte material according toExample 2.

In the X-ray diffraction pattern of Example 2, relatively intense peakswere observed at 2θ of 15.78, 31.32, 40.82, 48.72, 53.54, and 59.1degrees.

These peaks corresponded approximately to part of the peak positions ofthe X-ray diffraction pattern of an LYC phase with lattice constantsa=12.93 angstroms, b=11.20 angstroms, c=6.04 angstroms, α=90 degrees,β=90 degrees, and γ=90 degrees.

The relationship FWHM/2θ_(p) between the full width at half maximum(FWHM) and the peak central value 2θ_(p) of the peak at 2θ=31.32 degreeswas 0.63%.

A peak indicating the presence of a phase other than the first crystalphase, such as a diffraction peak derived from LiCl or a diffractionpeak derived from YCl₃, was not observed.

The ratio x_(L,Total)/x_(Y,Total) of the Li content to the Y content inthe solid electrolyte material according to Example 2 was 2.90. Thus,the solid electrolyte material according to Example 2 had a compositionformula including a Li-deficient first crystal phase represented by thecomposition formula Li_(2.95)Y_(1.02)Cl₆.

The solid electrolyte material according to Example 2 was used as asolid electrolyte used in a mixture and in a solid electrolyte layer.

Except for this, the production of a secondary battery and thecharge-discharge test were performed in the same manner as in Example 1.

The secondary battery according to Example 2 had an initial dischargecapacity of 532 μAh.

Example 3

Raw powders LiCl and YCl₃ of a solid electrolyte were mixed at a moleratio of LiCl:YCl₃=2.91:1.03.

Except for this mixing ratio and the Rietveld analysis described later,the synthesis, evaluation, and analysis were performed in the samemanner as in Example 1.

The ionic conductivity measured at 22° C. was 7.6×10⁻⁵ S/cm.

A sudden change in conductivity indicating a phase change (that is,phase transition) was not observed at a temperature in the range of −30°C. to 80° C.

FIG. 5 shows an XRD pattern of a solid electrolyte material according toExample 3.

In the X-ray diffraction pattern of Example 3, relatively intense peakswere observed at 2θ of 15.76, 31.32, 40.84, 48.70, 53.58, and 59.08degrees.

These peaks corresponded approximately to part of the peak positions ofthe X-ray diffraction pattern of an LYC phase with lattice constantsa=12.93 angstroms, b=11.20 angstroms, c=6.04 angstroms, α=90 degrees,β=90 degrees, and γ=90 degrees.

The relationship FWHM/2θ_(p) between the full width at half maximum(FWHM) and the peak central value 2θ_(p) of the peak at 2θ=31.32 degreeswas 0.58%.

In addition to the peaks derived from the first crystal phase, peaksderived from LiCl were observed at 2θ of 30.04, 34.84, and 50.14degrees.

The ratio x_(L,Total)/x_(Y,Total) of the Li content to the Y content inthe solid electrolyte material according to Example 3 was 3.0. Due tothe deposition of the LiCl phase, the ratio of the Li content to the Ycontent in the LYC phase was smaller than the total content ratio 3.0.Thus, the solid electrolyte material according to Example 3 contained aLi-deficient first crystal phase.

To determine the Li deficiency in the first crystal phase, the XRDpattern in FIG. 5 was subjected to the Rietveld analysis. RIETAN-FP (seeF. Izumi and K. Momma, “Three-dimensional visualization in powderdiffraction,” Solid State Phenom., 130, 15-20 (2007)) was used in theRietveld analysis. The phase 1 model structure was the LYC structure(space group Pnma) in which Yb was substituted by Y, and the phase 2model structure was LiCl (space group Fm-3m). The parameters of thescale factor, background function, and profile function and theparameters of the crystal structure were optimized by fitting. TheRietveld analysis showed that the phase fractions of the LYC phase andthe LiCl phase was x_(LYC):x_(LiCl)=0.79:0.21 based on the mole ratio.

From the evaluation results, the composition formula Li_(3−3δ)Y_(1+δ)Cl₆in the first crystal phase of the solid electrolyte material accordingto Example 3 was determined by calculating δ using the following formula(A1).

(x _(Li,Total) /x _(Y,Total))(1+δ)=x _(LiCl) /x _(LYC)+(3−3δ)  formula(A1)

Using the formula (A1), δ (Li deficiency was 36) in the first crystalphase of the solid electrolyte material according to Example 3 wascalculated to be 0.041. Thus, the solid electrolyte material accordingto Example 3 had a composition formula including a Li-deficient firstcrystal phase represented by the composition formulaLi_(2.88)Y_(1.04)Cl₆.

The solid electrolyte material according to Example 3 was used as asolid electrolyte used in a mixture and in a solid electrolyte layer.

Except for this, the production of a secondary battery and thecharge-discharge test were performed in the same manner as in Example 1.

The secondary battery according to Example 3 had an initial dischargecapacity of 540 μAh.

Example 4

Raw powders LiCl and YCl₃ of a solid electrolyte were mixed at a moleratio of LiCl:YCl₃=3:1.

Except for this, the synthesis, evaluation, and analysis were performedin the same manner as in Example 3.

The ionic conductivity measured at 22° C. was 8.0×10⁻⁵ S/cm.

A sudden change in conductivity indicating a phase change (that is,phase transition) was not observed at a temperature in the range of −30°C. to 80° C.

FIG. 5 shows an XRD pattern of a solid electrolyte material according toExample 4.

In the X-ray diffraction pattern of Example 4, relatively intense peakswere observed at 2θ of 15.78, 31.34, 40.84, 48.72, 53.56, and 59.10degrees.

These peaks corresponded approximately to part of the peak positions ofthe X-ray diffraction pattern of an LYC phase with lattice constantsa=12.91 angstroms, b=11.21 angstroms, c=6.04 angstroms, α=90 degrees,β=90 degrees, and γ=90 degrees.

The relationship FWHM/2θ_(p) between the full width at half maximum(FWHM) and the peak central value 2θ_(p) of the peak at 2θ=31.34 degreeswas 0.67%.

In addition to the peaks derived from the first crystal phase, peaksderived from LiCl were observed at 2θ of 30.04, 34.84, and 50.14degrees.

The ratio x_(L,Total)/x_(Y,Total) of the Li content to the Y content inthe solid electrolyte material according to Example 4 was 3.18.

The XRD pattern in FIG. 5 was subjected to the Rietveld analysis in thesame manner as in Example 3. The Rietveld analysis showed that the phasefractions of the LYC phase and the LiCl phase wasx_(LYC):x_(LiCl)=0.74:0.26 based on the mole ratio.

From the evaluation results, δ (Li deficiency was 36) of the compositionformula Li_(3−3δ)Y_(1+δ)Cl₆ in the first crystal phase of the solidelectrolyte material according to Example 4 was calculated to be 0.027using the formula (A1). Thus, the solid electrolyte material accordingto Example 4 had a composition formula including a Li-deficient firstcrystal phase represented by the composition formulaLi_(2.92)Y_(1.03)Cl₆.

The solid electrolyte material according to Example 4 was used as asolid electrolyte used in a mixture and in a solid electrolyte layer.

Except for this, the production of a secondary battery and thecharge-discharge test were performed in the same manner as in Example 1.

The secondary battery according to Example 4 had an initial dischargecapacity of 469 μAh.

Example 5

Raw powders LiCl and YCl₃ of a solid electrolyte were mixed at a moleratio of LiCl:YCl₃=3.3:0.9.

Except for this, the synthesis, evaluation, and analysis were performedin the same manner as in Example 3.

The ionic conductivity measured at 22° C. was 7.2×10⁻⁵ S/cm.

A sudden change in conductivity indicating a phase change (that is,phase transition) was not observed at a temperature in the range of −30°C. to 80° C.

FIG. 5 shows an XRD pattern of a solid electrolyte material according toExample 5.

In the X-ray diffraction pattern of Example 5, relatively intense peakswere observed at 2θ of 15.78, 31.32, 40.82, 48.70, 53.56, and 59.08degrees.

These peaks corresponded approximately to part of the peak positions ofthe X-ray diffraction pattern of an LYC phase with lattice constantsa=12.93 angstroms, b=11.20 angstroms, c=6.04 angstroms, α=90 degrees,β=90 degrees, and γ=90 degrees.

The relationship FWHM/2θ_(p) between the full width at half maximum(FWHM) and the peak central value 2θ_(p) of the peak at 2θ=31.32 degreeswas 0.54%.

In addition to the peaks derived from the first crystal phase, peaksderived from LiCl were observed at 2θ of 30.04, 34.84, and 50.14degrees.

The ratio x_(L,Total)/x_(Y,Total) of the Li content to the Y content inthe solid electrolyte material according to Example 5 was 3.92.

The XRD pattern in FIG. 5 was subjected to the Rietveld analysis in thesame manner as in Example 3. The Rietveld analysis showed that the phasefractions of the LYC phase and the LiCl phase wasx_(LYC):x_(LiCl)=0.50:0.50 based on the mole ratio.

From the evaluation results, δ (Li deficiency was 36) of the compositionformula Li_(3−3δ)Y_(1+δ)Cl₆ in the first crystal phase of the solidelectrolyte material according to Example 5 was calculated to be 0.010using the formula (A1). Thus, the solid electrolyte material accordingto Example 5 had a composition formula including a Li-deficient firstcrystal phase represented by the composition formulaLi_(2.97)Y_(1.01)Cl₆.

The solid electrolyte material according to Example 5 was used as asolid electrolyte used in a mixture and in a solid electrolyte layer.

Except for this, the production of a secondary battery and thecharge-discharge test were performed in the same manner as in Example 1.

The secondary battery according to Example 5 had an initial dischargecapacity of 528 μAh.

Example 6

Raw powders LiCl and YCl₃ of a solid electrolyte were mixed at a moleratio of LiCl:YCl₃=2.55:1.15.

Except for the mixing ratio and the Rietveld analysis conditions, thesynthesis, evaluation, and analysis were performed in the same manner asin Example 3.

The ionic conductivity measured at 22° C. was 2.6×10⁻⁴ S/cm.

A sudden change in conductivity indicating a phase change (that is,phase transition) was not observed at a temperature in the range of −30°C. to 80° C.

FIG. 5 shows an XRD pattern of a solid electrolyte material according toExample 6.

In the X-ray diffraction pattern of Example 6, relatively intense peakswere observed at 2θ of 15.76, 31.30, 40.78, 48.70, 53.46, and 59.08degrees. These peaks corresponded approximately to part of the peakpositions of the X-ray diffraction pattern of an LYC phase with latticeconstants a=12.94 angstroms, b=11.19 angstroms, c=6.05 angstroms, α=90degrees, β=90 degrees, and γ=90 degrees.

The relationship FWHM/2θ_(p) between the full width at half maximum(FWHM) and the peak central value 2θ_(p) of the peak at 2θ=31.30 degreeswas 0.67%.

In addition to the peaks derived from the first crystal phase, peaksderived from YCl₃ were observed at 2θ of 14.76, 26.42, and 32.84degrees.

The ratio x_(L,Total)/x_(Y,Total) of the Li content to the Y content inthe solid electrolyte material according to Example 6 was 2.37.

The XRD pattern in FIG. 5 was subjected to the Rietveld analysis. TheRietveld analysis was performed in the same manner as in Example 3except that YCl₃ (space group C2/m) was employed as the phase 2 modelstructure. The Rietveld analysis showed that the phase fractions of theLYC phase and the YCl₃ phase was x_(LYC):x_(YCl3)=0.94:0.06 based on themole ratio.

From the evaluation results, the composition formula Li_(3−3δ)Y_(1+δ)Cl₆in the first crystal phase of the solid electrolyte material accordingto Example 6 was determined by calculating δ using the following formula(A2).

(x _(Y,Total) /x _(Li,Total))(3−3δ)=x _(YCl3) /x _(LYC)+(1+δ)  formula(A2)

Using the formula (A2), δ (Li deficiency was 36) in the first crystalphase of the solid electrolyte material according to Example 6 wascalculated to be 0.088. Thus, the solid electrolyte material accordingto Example 6 had a composition formula including a Li-deficient firstcrystal phase represented by the composition formulaLi_(2.74)Y_(1.09)Cl₆.

The solid electrolyte material according to Example 6 was used as asolid electrolyte used in a mixture and in a solid electrolyte layer.

Except for this, the production of a secondary battery and thecharge-discharge test were performed in the same manner as in Example 1.

The secondary battery according to Example 6 had an initial dischargecapacity of 519 μAh.

Example 7

Raw powders LiCl and YCl₃ of a solid electrolyte were mixed at a moleratio of LiCl:YCl₃=2.25:1.25.

Except for this, the synthesis, evaluation, and analysis were performedin the same manner as in Example 6.

The ionic conductivity measured at 22° C. was 1.8×10⁻⁴ S/cm.

A sudden change in conductivity indicating a phase change (that is,phase transition) was not observed at a temperature in the range of −30°C. to 80° C.

FIG. 5 shows an XRD pattern of a solid electrolyte material according toExample 7.

In the X-ray diffraction pattern of Example 7, relatively intense peakswere observed at 2θ of 15.80, 31.32, 40.8, 48.74, 53.48, and 59.12degrees. These peaks corresponded approximately to the X-ray diffractionpeak positions of an LYC phase with lattice constants a=12.94 angstroms,b=11.18 angstroms, c=6.05 angstroms, α=90 degrees, β=90 degrees, andγ=90 degrees.

The relationship FWHM/2θ_(p) between the full width at half maximum(FWHM) and the peak central value 2θ_(p) of the peak at 2θ=31.32 degreeswas 0.67%.

In addition to the peaks derived from the first crystal phase, peaksderived from YCl₃ were observed at 2θ of 14.76, 26.42, and 32.84degrees.

The ratio x_(L,Total)/x_(Y,Total) of the Li content to the Y content inthe solid electrolyte material according to Example 7 was 1.94.

The XRD pattern in FIG. 5 was subjected to the Rietveld analysis in thesame manner as in Example 6. The Rietveld analysis showed that the phasefractions of the LYC phase and the YCl₃ phase wasx_(LYC):x_(YCl3)=0.83:0.17 based on the mole ratio.

From the evaluation results, δ (Li deficiency was 36) of the compositionformula Li_(3−3δ)Y_(1+δ)Cl₆ in the first crystal phase of the solidelectrolyte material according to Example 7 was calculated to be 0.133using the formula (A2). Thus, the solid electrolyte material accordingto Example 7 had a composition formula including a Li-deficient firstcrystal phase represented by the composition formulaLi_(2.60)Y_(1.13)Cl₆.

The solid electrolyte material according to Example 7 was used as asolid electrolyte used in a mixture and in a solid electrolyte layer.

Except for this, the production of a secondary battery and thecharge-discharge test were performed in the same manner as in Example 1.

The secondary battery according to Example 7 had an initial dischargecapacity of 478 μAh.

Comparative Example 1

Raw powders LiBr and InBr₃ were weighed at a mole ratio ofLiBr:InBr₃=3:1 in a dry atmosphere with a dew point of −30° C. or less.The raw powders were ground and mixed in a mortar. The sample waspressed into pellets, was put into a glass tube under vacuum, and wasfired at 200° C. for one week.

Thus, a solid electrolyte material Li₃InBr₆ according to ComparativeExample 1 was prepared.

Except for this, the ionic conductivity and phase transition wereevaluated in the same manner as in Example 1.

The ionic conductivity measured at 22° C. was less than 1×10⁻⁷ S/cm.

FIG. 4 shows the temperature dependence of ionic conductivity of thesolid electrolyte material according to Comparative Example 1.

As shown in FIG. 4, the conductivity changed rapidly at approximately55° C. during temperature rise due to the temperature dependence ofconductivity. Thus, a phase change was observed in the solid electrolytematerial according to Comparative Example 1.

Comparative Example 2

Raw powders LiCl and FeCl₂ of a solid electrolyte were mixed at a moleratio of LiCl:FeCl₂=2:1. Thus, a solid electrolyte material Li₂FeCl₄according to Comparative Example 2 was prepared.

Except for this, the ionic conductivity was evaluated in the same manneras in Example 1.

The measured ionic conductivity was 8.7×10⁻⁶ S/cm.

The solid electrolyte material according to Comparative Example 2 wasused as a solid electrolyte used in a mixture and in a solid electrolytelayer.

Except for this, the production of a secondary battery and thecharge-discharge test were performed in the same manner as in Example 1.

FIG. 6 shows the initial discharging characteristics of the secondarybattery according to Comparative Example 2.

The secondary battery according to Comparative Example 2 had an initialdischarge capacity of less than 1 μAh. In other words, thecharge-discharge operation of the secondary battery according toComparative Example 2 could not be observed.

Table 1 shows the structures and evaluation results of Examples 1 to 7and Comparative Examples 1 and 2.

TABLE 1 Li/Y ratio in Initial Total Li/Y first crystal discharge ratio(total phase Conductivity Phase capacity composition) XRD peak Crystalphase (composition) FWHM/2θ_(p) (S/cm) transition (μAh) Example 1 2.6215.74°, 31.28°, 40.76°, 48.68°, First crystal 2.62 0.68% 3.0e−4 No 596(Li_(2.80)Y_(1.07)Cl₆) 53.46°, 59.08° phase single(Li_(2.80)Y_(1.07)Cl₆) phase Example 2 2.90 15.78°, 31.32°, 40.82°,48.72°, First crystal 2.90 0.63% 1.8e−4 No 532 (Li_(2.95)Y_(1.02)Cl₆)53.54°, 59.1° phase single (Li_(2.95)Y_(1.02)Cl₆) phase Example 3 3.015.76°, 31.32°, 40.84°, 48.70°, First crystal 2.76 0.58% 7.6e−5 No 540(Li₃Y₁Cl₆) 53.58°, 59.08°, and, 30.04°, phase + LiCl(Li_(2.88)Y_(1.04)Cl₆) 34.84°, 50.14° phase Example 4 3.18 15.78°,31.34°, 40.84°, 48.72°, First crystal 2.84 0.67% 8.0e−5 No 469(Li_(3.09)Y_(0.97)Cl₆) 53.56°, 59.10°, and, 30.04°, phase + LiCl(Li_(2.92)Y_(1.03)Cl₆) 34.84°, 50.14° phase Example 5 3.92 15.78°,31.32°, 40.82°, 48.70°, First crystal 2.94 0.54% 7.2e−5 No 528(Li_(3.40)Y_(0.87)Cl₆) 53.56°, 59.08°, and, 30.04°, phase + LiCl(Li_(2.97)Y_(1.01)Cl₆) 34.84°, 50.14° phase Example 6 2.37 15.76°,31.30°, 40.78°, 48.70°, First crystal 2.51 0.67% 2.6e−4 No 519(Li_(2.65)Y_(1.12)Cl₆) 53.46°, 59.08°, and, 14.76°, phase +YCl₃(Li_(2.74)Y_(1.09)Cl₆) 26.42°, 32.84° phase Example 7 1.94 15.80°,31.32°, 40.80°, 48.74°, First crystal 2.30 0.67% 1.8e−4 No 478(Li_(2.36)Y_(1.22)Cl₆) 53.48°, 59.12°, and, 14.76°, phase + YCl3(Li_(2.60)Y_(1.13)Cl₆) 26.42°, 32.84° phase Comparative Li₃InBr₆ N/AUnidentified N/A N/A  <1e−7 Yes — example 1 Comparative Li₂FeCl₄ N/ASpinel structure N/A N/A 8.7e−6 No  <1 example 2

DISCUSSION

A comparison of Examples 1 to 7 with Comparative Examples 1 and 2 showsthat the solid electrolyte materials including the Li_(3−3δ)Y_(1+δ)Cl₆crystal phase with a Li:Y mole ratio of less than 3 have a high ionicconductivity of 5×10⁻⁵ S/cm or more near room temperature. It also showsthat no phase transition occurs at a temperature in the range of −30° C.to 80° C. Thus, Examples 1 to 7 have a stable structure in the expectedoperating temperature range of the battery.

In particular, Examples 1 and 2 show that the solid electrolyte materialincluding as a single phase the first crystal phase with a Li:Y moleratio of less than 3 has a stable structure in the expected operatingtemperature range of the battery and has high ionic conductivity.

Examples 3 to 5 show that a Li:Y mole ratio of 3 (Example 3) or morethan 3 (Examples 4 and 5) in the solid electrolyte material results inthe deposition of the LiCl phase and that the solid electrolyte materialincluding the first crystal phase with a Li:Y mole ratio of less than 3has a stable structure in the expected operating temperature range ofthe battery and has high ionic conductivity.

Examples 6 and 7 show that the solid electrolyte material with a Li:Ymole ratio of less than 3 has a stable structure in the expectedoperating temperature range of the battery and has high ionicconductivity even in the presence of a phase other than the firstcrystal phase.

In Examples 1 to 7, the battery performed the charge-discharge operationat room temperature. By contrast, Comparative Example 2 had littledischarge capacity and could not perform the battery operation.Furthermore, the materials according to Examples 1 to 7 contained nosulfur as a constituent element and generated no hydrogen sulfide.

Consequently, the solid electrolyte material according to the presentdisclosure generates no hydrogen sulfide and can stably maintain highlithium ion conductivity.

What is claimed is:
 1. A solid electrolyte material comprising: a firstcrystal phase, wherein the first crystal phase has a composition that isdeficient in Li as compared with a composition represented by thefollowing composition formula (1):Li₃Y₁Cl₆.
 2. The solid electrolyte material according to claim 1,wherein the first crystal phase is represented by the followingcomposition formula (2):Li_(3−3δ)Y_(1+δ)Cl₆, where0≤δ≤0.15.
 3. The solid electrolyte material according to claim 2,wherein0.01≤δ≤0.133.
 4. The solid electrolyte material according to claim 1,wherein the solid electrolyte material has an X-ray diffraction patternthat includes a peak in each of a first range, a second range, and athird range, the X-ray diffraction pattern being measured using Cu-Kαradiation as an X-ray source, in the first range, a diffraction angle 2θis 30.34 degrees or more and 32.36 degrees or less, in the second range,the diffraction angle 2θ is 39.51 degrees or more and 42.07 degrees orless, and, in the third range, the diffraction angle 2θ is 47.18 degreesor more and 50.30 degrees or less.
 5. The solid electrolyte materialaccording to claim 4, wherein the X-ray diffraction pattern furtherincludes a peak in a fourth range in which the diffraction angle 2θ is15.2 degrees or more and 16.23 degrees or less and in a fifth range inwhich the diffraction angle 2θ is 52.4 degrees or more and 54.6 degreesor less.
 6. The solid electrolyte material according to claim 4, whereinthe X-ray diffraction pattern satisfies FWHM/2θ_(p)≤0.01, where FWHMdenotes a full width at half maximum of the peak in the first range, and2θ_(p) denotes a central value of the peak.
 7. The solid electrolytematerial according to claim 1, wherein the first crystal phase containsa chlorine sublattice, and the chlorine sublattice has an arrangement ofchlorine that includes an atomic arrangement of a distorted hexagonalclose-packed structure.
 8. The solid electrolyte material according toclaim 1, wherein the first crystal phase contains an atomic arrangementof a Li₃YbCl₆ structure.
 9. The solid electrolyte material according toclaim 1, wherein the solid electrolyte material has an X-ray diffractionpattern that includes a peak in at least one range selected from thegroup consisting of a range in which a diffraction angle 2θ is 29.18degrees or more and 31.03 degrees or less and a range in which thediffraction angle 2θ is 33.83 degrees or more and 36.00 degrees or less,the X-ray diffraction pattern being measured using Cu-Kα radiation as anX-ray source.
 10. The solid electrolyte material according to claim 9,further comprising a second crystal phase, wherein the second crystalphase has a LiCl parent structure.
 11. The solid electrolyte materialaccording to claim 1, wherein the solid electrolyte material has anX-ray diffraction pattern that includes a peak in at least one rangeselected from the group consisting of a range in which a diffractionangle 2θ is 14.34 degrees or more and 15.23 degrees or less and a rangein which the diffraction angle 2θ is 25.65 degrees or more and 27.26degrees or less, the X-ray diffraction pattern being measured usingCu-Kα radiation as an X-ray source.
 12. The solid electrolyte materialaccording to claim 11, further comprising a third crystal phase, whereinthe third crystal phase has a YCl₃ parent structure.
 13. A batterycomprising: the solid electrolyte material according to claim 1; apositive electrode; a negative electrode; and an electrolyte layerbetween the positive electrode and the negative electrode, wherein atleast one selected from the group consisting of the positive electrode,the negative electrode, and the electrolyte layer contains the solidelectrolyte material.